1. Field of the Invention
The present invention relates to an optical disk driver for driving and controlling an optical disk recording medium.
2. Description of the Related Art
Recent rapid technological innovation in the fields of information processing technology leads to necessity of large-capacity storage media. In this situation, optical disk recording media have attracted attention as small-size, low-cost, and large-capacity storage media.
FIG. 12 shows the configuration of a conventional optical disk driving apparatus. In the apparatus of FIG. 12, a reference numeral 101 indicates an optical disk storage medium on which data of about 500 megabytes can be recorded with a fixed surface density. A numeral 102 denotes an actuator including an optical unit to read data from the medium 101 and a device to drive the optical unit 102. A numeral 103 represents a spindle motor to rotate the optical disk 101. A numeral 104 stands for a servo circuit to accomplish a servo control operation for the driver of the actuator 102 and a servo control operation to rotate the spindle motor 103 at a fixed linear speed. A numeral 105 designates a signal processing circuit to decode a signal obtained from the optical unit of the actuator 102 and conducts error correction for the decoded signal so as to resultantly produce data therefrom. A numeral 106 indicates a central processing unit (CPU) to control the overall operation of the optical disk driver.
Description will be now given of operations in a successive information reproducing operation and a disk accessing operation of the conventional optical disk driver thus constructed.
In the successive information reproduction, the servo circuit 104 controls a position of the actuator 102 in a focusing direction (denoted by an arrow F in FIG. 12) and a tracking direction (as indicated by an arrow T therein) of the actuator 102 such that the optical unit of the actuator 102 follows a track of the optical disk 101. At the same time, to read data written on the optical disk 101 with a fixed surface density, the servo circuit 104 controls the spindle motor 103 to rotate at a fixed linear speed. The signal attained from the optical unit of the actuator 102 is fed to the signal processing circuit 105. The circuit 105 decodes the signal and then corrects errors thereof so as to thereby produce a digital signal.
On the other hand, in the accessing stage (of the track seeking operation), there is employed a short jump or a long jump according to the number of tracks through which the actuator is to be moved. Namely, the short jump is used when only the optical unit is moved in the actuator 102, whereas the long jump is adopted to move the actuator 102.
Since the mass of the optical unit is small and the quantity in change of the spindle motor rotating speed is quite small, the short jump can be conducted in a relatively short period of time. However, in the long jump, a long period of time is required from when the actuator 102 is activated to be moved to when the actuator 102 is completely positioned at its destination because of the large mass of the actuator 102 and the large quantity in change of the motor rotating speed.
Consequently, to increase the operation speed of the optical disk driving apparatus (particularly, of an information searching facility), it is necessary to reduce the period of time to achieve the long jump when locating the actuator over destined tracks in the track accessing operation.
Analyzing the period of time necessary to move the actuator to the destination, there is required, even after the movement of the actuator is finished, a long period of time is required until the operation to appropriately control the rotating speed of the spindle motor is terminated. Namely, before the rotary speed of the motor is fixed to the desired linear speed, the actuator cannot read the data recorded on the disk at a fixed surface density. Therefore, the actuator enters the wait state and stays therein until the predetermined linear speed is developed. In other words, there occurs a wait period of time before a constant linear speed is obtained for the pertinent track of the optical disk.
Furthermore, to decrease the time required to control the rotating speed of the spindle motor, it is necessary to increase torque of the spindle motor, which leads to increase in the size and consumption power thereof. These problems inevitably occur especially when the transfer rate is desired to be increased, for example, by use of a quadruple-speed disk driving apparatus.